INNOVATIVE DRILLED SHAFT INSTALLATION PROCESS THROUGH EXISTING BRIDGE FOUNDATIONS Tracy Brettmann, P.E., D.GE, Executive Vice President A. H. Beck Foundation Company, Houston, Texas ABSTRACT The Highway 146 Bridge Expansion Project across the Clear Creek Channel in Houston, Texas was designed on driven precast concrete piles. However, during construction, the piles along one side of the bridge along the main channel encountered obstructions and couldn’t be installed. These obstructions turned out to be the remnants of a previous bridge foundation at this location, which was unknown to the designers since that bridge had been demolished 40 years ago. Those old foundations were massive 20 ft by 40 ft (6 m by 12 m) pile caps 11 ft (3.3 m) thick supported on precast concrete piles 37 to 55 ft (11 to 17 m) long. The foundation re-design for these locations involved installing a single 78 inch (2 m) diameter drilled shaft up to 125 ft (38 m) long to replace the originally planned driven pile supported pile cap. The drilled shafts would need to be installed within very tight tolerances since they were supporting a single bridge column directly above it. In addition to drilling through the obstructions, this work would need to be completed from barges in 30 ft (9 m) of water capable of dealing with both the current and tides affecting this area. The shafts were installed using a multi-step process. The first step involved coring a larger diameter 98 inch (2.5 m) hole through the reinforced concrete pile cap and removing the concrete inside. This was followed by the installation of a permanent casing to 65 ft (20 m) and removing the soil and existing precast piles inside. Finally, the drilled shaft excavations were advanced to the completion depths (uncased) using bentonite slurry as the support fluid. Keywords: drilled shafts, obstruction drilling, casing rotator, marine work, bridge foundation INTRODUCTION The expansion of a 4 mile (6.5 km) long heavily congested segment of State Highway 146 was done to improve mobility and safety, reduce traffic congestion, improve hurricane evacuation measures, and provide travel options while reducing adverse environmental effects. The middle of the project consisted of a 4 lane bridge (2 in each direction) over the Clear Creek Channel as shown in Figure 1. The main source of the traffic congestion was an intersection near the south side of the bridge. The 4 lane highway was expanded to a 6 lane freeway with express lanes added over Clear Creek. This required both the building of a new bridge for the express lanes adjacent to the existing bridge and expansion of the existing bridge for local traffic acting as a frontage road. The area right around the bridge is a major local tourist destination due to the Kemah Boardwalk development containing dozens of restaurants, shops and amusement rides. The Clear Creek Channel is also heavily used supporting a large commercial shrimp industry and is home to the third largest recreational boating fleet in the United States. Re-Print: Conference Technical Paper DFI-EFFC International Conference Berlin - May 2022 1
INNOVATIVE DRILLED SHAFT INSTALLATION PROCESS THROUGH EXISTING BRIDGE FOUNDATIONS
Jun 18, 2023
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